$$U_{280}(x, y) = \frac{- y - \sqrt{- 4 x^{2} + y^{2} - 2 y + 1} + 1}{2 x^{2}}$$

$$T_{280}(n, m, k) = \frac{k \left(\left(-1\right)^{n} + 1\right) {\binom{k + n}{\frac{n}{2}}} {\binom{k + m + n - 1}{m}}}{2 k + 2 n}$$